What I think that people are missing here is that the auto button is not the "automatic blower control" only. In auto mode the system adjusts the temperature of the heat exchangers as well as the fan speed to obtain the desired setting indicated by the thumbwheel. The further apart the actual and desired temperatures are the higher the fan speed will be. By design once the desired and actual temps are close the blower slows way down. If your climate control doesn't function this way then fixing it will be a lot cheaper and easier than re-engineering some half assed way to make it work like it's not supposed to.

The first thing that I would check is the function of the cabin air temperature sensor located in sunroof/dome light switch. LarryBible suggests holding a small piece of paper (.25" square maybe) up to it to see if it will hold the paper (ie, air being sucked into it)

A non- or malfunctioning cabin air temp sensor would cause your CC unit to do wacky things like blow too much or all the time.

First off I must say that the Mercedes Auto AC is a complicated system that being said it is equally expensive and time consuming to repair. Who really needs "Auto Air" . I WANT AC THAT RESPONDS TO MY NEEDS and not a $500 - $2000.00 repair bill every 2 - 5 years and I’m sure many others don't want that either. I repaired the AC in my benz doing the work myself and spent over $300.00 for parts and hours studing schematics and components. I repaired my BMW AC for less than $100.00 It needed twice as much work due to previous owners neglect but was much easier to repair.

The solution if well thought out can be quite simple. Most AC controls for most vehicles simply turn on a compressor and let you control the blower speed and air mixture.

I typically do not do things "HALF ASS". I have solved many applications for factories and companies all over the world for the past 10 years in factory automation, web control and automated packaging to name a few and have designed and built several machines worth over $500,000.00. I have redesigned many systems for CNC machines that were too complex and too expensive to repair. For example; a failed power supply. 750.00 to replace OE I did it for 29.95 and works just as good if not better with added surge suppression that I incorporated.

I know what I am doing and I always try to think of the best solution for the investment return as well as long term safety and reliability.

I do appreciate your input no matter how negative it might be. I have taken apart my Climate Controller, AC relay used a scope and voltmeter to diagnose my problems and have even reversed engineered the AC relay. I have spent many hours studying the MB Auto AC system and find it too complex for the simple operation it does. It's a "cool" (no pun intended) system and for the MB diehards that want all OE maybe its not for them. But for the others out there that just want their AC to Work, like myself, I think I can come up with a solution.


If I can come up with a simple safe inexpensive solution I believe MB owners will beat a path to my door. It sounds like a challenge to me and I love challenges.

Again thank you again Craig, duxthe1 and skiier3_9 for your posts!

Anthony Bridges

Something like this:

http://catalog.peachparts.com/item.wws?catpk=&sku=227550999

my auto mode works. I can hear and feels fan speed when it reaches desired temp. BUT if I want to keep fan in medium setting, thats what I want and its not for my climate control to choose it. MB auto climate control is very well designed but I never used it. I just want to have medium fan setting. If you can provide some details how to modify climate control unit please let us know. Hope this moment will happen soon. Keep up great work.
Thnak you
Victor

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1999 ML430 Silver 135k ml
Smoked LED taillights, Alpine in-dash DVD player, 12" sub, Pioneer components, 2 amps, 4200k HIDs, ML55 headlights, 20" rims, mirror LED blinkers

SOLD. 1996 E320 145k ml. Burgundy

SOLD but miss it everyday 1992 500sel Black
Chime buzzer mod,Alpine CD/MP3 player with stock amp,Euro headlights,S600 grill,20" rims, BEST CAR EVER!

SOLD. 1990 300E White
187k ml,smoked tails,Euro headlights,17rims,Intake,12" sub in first aid kit,alarm/autostart,buzzer mod

The easiest way would be to sacrifice the low speed switch, change the blower resistor for that speed to a smaller value and then the fan would run faster when you select that speed. You;d have to experiment with different resistor values to get the one you want, or just put a wirewound pot in place of the resistor, and when you get the speed you like, measure the resistance of the pot and then replace the old resistor with that value.

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Theo

1985 300D turbo 235K miles, Delvac 1, mostly B20 BioDiesel

klakka klakka klakka klakka...Arf arf arf arf...
How does that dog always know when Theo's home??!

It is going to take mw a better part of a week to finish this project.

I have 2 modification ideas.

W124 climate control blower motor modification.

1. Using the fader control position to install a variable resistor for infinite speed control. Both mods will only work on climate control systems that are working. This will not make your fan work if it is not currently working nor will it correct improper vent or heating/cooling operations.

2. Sacrificing the Auto button for a medium speed or include a small switch that will allow both that can be installed in glove box or under dash..

I would expect a cost of around $20.00 - $30.00 for a full color instruction manual or CD with lots of pictures along with all the components needed to do this modification.

What do you think ?tgantos , Victor300E

I don't know about using the auto position. It's a different circuit, and very complicated/convoluted from my first glance at the schematic. I would not want to have a solution requiring a complete redesign of the present pre-cmos logic. So I still think using the low speed position is probably your best option, but like I said I just glanced at the schematic. Now if you want to redesign the whole system and build a new controller for everything, using modern electronics, then you may have a market if you can get the price down around $300.

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Theo

1985 300D turbo 235K miles, Delvac 1, mostly B20 BioDiesel

klakka klakka klakka klakka...Arf arf arf arf...
How does that dog always know when Theo's home??!

Why not use the low speed button for both low and medium using, as you stated earlier, a switch under the dash or glove box that would allow the changing of impedence or resistance to the motor?
Chris

If you can do this I would be all over it!!

__________________
94 E320 with:
18" ///AMG Monoblock II's,AMG Gen II front bumper, H&R spings,500E sway bar, Bilstein sports, Eisemann Exhst, K&N,E500 Headlamps, Crystal Clear Corners, Avantgard Grill ...and more stuff to come! oh yeah 241k miles!!


My Car WOO HOO...... Now SOLD
New car.... 2001 Jaguar XJR!!!!

Why not leave it factory............and use the temperture wheel to regulate the fan speed

Best idea so far, easiest to do, and doesn't cripple the system.

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Theo

1985 300D turbo 235K miles, Delvac 1, mostly B20 BioDiesel

klakka klakka klakka klakka...Arf arf arf arf...
How does that dog always know when Theo's home??!

Have you a solution Anthony with the anemic low fan speed on the 124??
The other issue on this terrible MB climate system is the one heat setting fits all on defrost. I have to continuously switch on and off to regulate the temperature in the cabin when defrost is switchted on.
Thanks - Tom

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'96 C220 138,000mi, '95 E300D 239,000 mi., '87 300TD 214,000mi '88 6.2 Turbo Diesel Chevy Conversion Van 253,000 mi.

I have a 94 wagon and a 95 sedan. Both have what I believe are fully functional climate control systems. With the high blower setting you get hurricane force winds inside the car, with the low blower setting the air flow is barely noticeable. Auto is a crap shot. I read in the manual that with defrost and auto selected, fan speed is dependent on coolant temperature. Not sure what auto is supposed to do with normal cooling or heating. I suspect that a large temp difference between selected and actual should result in higher fan speed, but the manual doesn't really say. Also, at high outside temperature, recirc is automatically selected. This usually results in higher airflow contributing to the internal hurricane.

Does anybody know how auto is supposed to work?